[FAB-10538]: Fix gossip scatter of pvt data
[FAB-10538]: Fix gossip scatter of pvt data

Currently while scattering pull request via gossip with digests of
private data, same digest repeating several times and other digests of
missing private data of other transactions from the block just ignored.
This commit fixes scattering procedure to avoid repetitions in same pull
request and also to efficiently retrieve all missing data from one peer
within same request.

Change-Id: If6287b1b04319a9ddc5937c09d0eec4d60f55e2d
Signed-off-by: Artem Barger <6d127d713cb520aa658cf81ac2373d74ffc1958c@il.ibm.com>

stemlending/fabric,stemlending/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,hyperledger/fabric,jimthematrix/fabric,xixuejia/fabric,manish-sethi/fabric-sidedb,muralisrini/fabric,xixuejia/fabric,binhn/fabric,jimthematrix/fabric,binhn/fabric,binhn/fabric,manish-sethi/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,muralisrini/fabric,manish-sethi/fabric-sidedb,xixuejia/fabric,muralisrini/fabric,manish-sethi/fabric,manish-sethi/fabric-sidedb,hyperledger/fabric,stemlending/fabric